High-power solid state relay employing photosensitive current augmenting means for faster turn-on time

Abstract

A high-power solid state relay uses optically-controlled shunt and series solid state switches between a photodiode array and an output device to provide enhanced turn-off and transient immunity characteristics and an optically-controlled charging network connected to the switched load to enhance the turn-on characteristics of the relay.

What is claimed is: 
     
       1. A solid state relay comprising: a semiconductor switch having an output;   a photovoltaic array for maintaining the switch in its on-state when illuminated;   photoresponsive means for augmenting current from the photovoltaic array with current from the switch output only during initial illumination of the photovoltaic array; and   illumination means for illuminating both the photovoltaic array and the photoresponsive augmentation means.   
     
     
       2. A solid state relay as recited in claim 1 wherein the photoresponsive augmentation means comprises a plurality of phototransistors. 
     
     
       3. A solid state relay responsive to light comprising: a photodiode array for generating a voltage when illuminated;   a solid state switch responsive to the photodiode array voltage for switching an output voltage, the solid state switch having an inherent input capacitance;   photoresponsive series switch means for coupling and decoupling the solid state switch to the photodiode array in response to light; and   current generator means coupled to the solid state switch the current generator means producing a photocurrent in response to light for charging the inherent capacitance, the current generator means further comprising amplification means for amplifying the photocurrent.   
     
     
       4. A solid state relay as recited in claim 3 wherein the amplification means amplifies the photocurrent only while the solid state switch is in an off-state. 
     
     
       5. A solid state relay as recited in claim 4 wherein the current generator means comprises a plurality of phototransistors, the phototransistors being biased by a output across the output of the solid state switch. 
     
     
       6. A solid state relay as recited in claim 3 wherein the solid state switch comprises a field effect transistor (FET). 
     
     
       7. A solid state relay as recited in claim 6 wherein the current generator means comprises a plurality of phototransistors connected between the gate and drain of the output FET. 
     
     
       8. A solid state relay as recited in claim 3 wherein the solid state switch comprises first and second output field effect transistors (FETs) connected gate to gate and source to source, the drains of each FET being connectable to an output voltage. 
     
     
       9. A solid state relay as recited in claim 8 wherein the current generator means comprises an array of phototransistors connected between the gates and the drains of the output FETs. 
     
     
       10. A solid state relay as recited in claim 9 wherein the current generator means further comprises rectifying means coupling the phototransistor array to the drains of the output FETs. 
     
     
       11. A solid state relay comprising: a semiconductor switch for switching a voltage and having a control terminal and an inherent input capacitance;   a photovoltaic array coupled to the switch for closing the switch upon illumination of the photovoltaic array;   shorting means coupled to the switch for accelerating discharge of the inherent capacitance when illumination of the photovoltaic array is discontinued;   charging means for accelerating the charging of the inherent capacitance upon illumination of the photovoltaic array comprising phototransistor means for coupling the switched voltage to the control terminal of the switch; and   illumination means for simultaneously illuminating the photovoltaic array and the phototransistor means.   
     
     
       12. A solid state relay comprising: a solid state light emitter;   a solid state photodetector optically coupled to the light emitter;   a variable impedence solid state switch having a control input coupled to the solid state photodetector and being connectable to a switched load circuit, the solid state switch providing a low impedence path in the switched load circuit while in an on-state and a high impedence path while in an off-state;   a solid state current generator having a drain and a source, the source being coupled to the control input of the variable impedence solid state switch and the drain being coupled to the switched load circuit.   
     
     
       13. A solid state relay as recited in claim 12 wherein the solid state current generator is light sensitive and is optically coupled to the solid state light emitter. 
     
     
       14. A solid state relay as in claim 13 wherein the solid state current generator comprises a phototransistor array biased by the voltage in the switched load circuit across the solid state variable impedence switch. 
     
     
       15. A solid state relay as in claim 14 wherein the solid state current generator further comprises a voltage rectifier coupled between the phototransistor array and the switched load circuit across the solid state variable impedence switch for coupling the highest voltage potential across the variable impedence switch to the phototransistor array. 
     
     
       16. A solid state relay as in claim 12 further comprising series switch means controllable by light and optically coupled to the light emitting means, the series switch means being connected between the solid state photodetector and the control input of the solid state variable impedence switch for selectably coupling or decoupling the photodetector to the variable impedence switch. 
     
     
       17. A solid state relay comprising: a light emitting diode connectable to a control circuit;   a primary photodiode array optically coupled to the light emitting diode and having first and second terminals, the primary photodiode array having a voltage potential generated across the first and second terminals in response to illumination from the light emitting diode such that the first terminal provides a higher voltage relative to the second terminal;   a secondary photodiode array optically coupled to the light emitting diode and having first and second terminals, the secondary photodiode array having a voltage potential generated across the first and second terminals in response to illumination from the light emitting diode such that the first terminal provides a higher voltage relative to the second terminal;   a first output double diffused MOS (DMOS) junction field effect transistor (JFET) connectable to a load circuit having gate, source and drain electrodes;   a second output double diffused MOS (DMOS) junction field effect transistor (JFET) connectable to a load circuit having gate, source and drain electrodes, the gate being connected to the gate electrode of the first output transistor, the source being connected to the source electrode of the first output transistor;   a first pnp phototransistor optically coupled to the light emitting diode and having base, emitter and collector electrodes, the collector being connected to the gate eletrodes of the first and second output transistors and the emitter being connected to the first terminal of the primary photodiode array;   a second pnp phototransistor optically coupled to the light emitting diode and having base, emitter and collector electrodes, the emitter being connected to the source electrodes of the first and second output transistors and the collector being connected to the second terminal of the photodiode array;   a silicon controlled rectifier (SCR) comprised of a npn bipolar transistor and a pnp bipolar transistor each having base, emitter and collector electrodes, the base of the pnp bipolar transistor being connected to the collector electrode of the npn bipolar transistor and the first terminal of the primary photodiode array, the emitter of the pnp bipolar transistor being connected to the gate electrodes of the first and second output transistors, the base of the npn bipolar transistor being connected to the collector electrode of the pnp bipolar transistor and the second terminal of the primary photodiode array, and the emitter of the npn transistor being connected to the source electrodes of the first and second output transistors;   a junction field effect transistor (JFET) with gate, source and drain electrodes, the drain electrode being connected to the gate electrodes of the first and second output transistors and the source electrode being connected to the sources electrodes of the first and second output transistors;   a first blocking diode having an anode and a cathode, the cathode being connected to the drain electrode of the first output transistor;   a second blocking diode having an anode and a cathode, the cathode being connected to the drain electrode of the second output transistor and the anode being connected to the anode of the first blocking diode; and   a phototransistor array optically coupled to the light emitting diode and comprising a plurality of phototransistors connected serially, one end of the array being connected to the gate electrodes of the first and second output transistors, the other end of the array being connected to the anodes of the first and second blocking diodes.